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The concave X-ray spectrum of the blazar ON 231: the signature of intermediate BL Lac objects
G. Tagliaferri, G. Ghisellini, P. Giommi +17
ON 231 was observed with BeppoSAX in May and June 1998, following an exceptional optical outburst which occured in April--May. We measured the X-ray spectrum from 0.1 up to 100 keV…
Isolated Neutron Stars: Accretors and Coolers
Aldo Treves, Roberto Turolla, Silvia Zane +1
As many as neutron stars populate the Galaxy, but only are directly observed as pulsars or as accreting sources in X-ray binaries. In principle also the accre…
The HST Survey of BL Lacertae Objects. I. Surface Brightness Profiles, Magnitudes, and Radii of Host Galaxies
Riccardo Scarpa, C. Megan Urry, Renato Falomo +2
We report on a large HST imaging survey of BL Lac objects, at spatial resolution ~10 times better than previous ground-based surveys. We focus on data reduction and analysis, descr…
The HST Survey of BL Lacertae Objects. II. Host Galaxies
C. Megan Urry, Riccardo Scarpa, Matthew O'Dowd +3
We have used the HST WFPC2 camera to survey 132 BL Lac objects comprising seven complete radio-, X-ray-, and optically-selected samples. We obtained useful images for 110 targets s…
The Neutron Stars Census
S. B. Popov, M. Colpi, A. Treves +3
The paucity of old isolated accreting neutron stars in ROSAT observations is used to derive a lower limit on the mean velocity of neutron stars at birth. The secular evolution of t…
HST Observations of BL Lacertae Environments
J. E. Pesce, C. M. Urry, M. O'Dowd +3
We analyze images of BL Lacertae objects obtained with the {\it Hubble Space Telescope} WFPC2 and the F814W filter. The nine objects cover a redshift range of 0.19 to 0.997. The re…